Flocculation of kaolin slurries with phosphoric acid

ABSTRACT

A process for improving the viscosity and slurry stability of leached kaolin clays, and the improved products thus formed are disclosed. The process involves the addition of phosphoric acid as a clay flocculant to a clay slurry during leaching with known leaching compounds, such as compounds containing an active (S2O4) group, to yield a finished clay product that, upon dispersion, possesses a lowe viscosity and improved slurry stability. Through the practice of the invention, a washing step and/or a second filtration step, sometimes considered necessary in conventional kaolin processing for removal of excess soluble salts to obtain minimum viscosities and adequate slurry stability, is obviated.

nite States Patent 9] Abercrombie, Jr.

[ F LOCCULATION OF KAOLIN SLURRIES WITH PHOSPHORIC ACID [75] Inventor: William F. Abercrombie, Jr., Macon, Ga.

[73] Assignee: J. M. Huber Corporation, Huber,

22 Filedz- July 2, 1973 211 App]. No.: 375,636

[52] US. Cl. 106/288 B, 106/72, 106/308 B,

3,399,960 9/1968 Conley .111. 106/72 Primary Examiner-Delbert E. Gantz Assistant Examiner-J. V. Howard Attorney, Agent, or Firm-Pravel & Wilson [5 7] ABSTRACT A process for improving the viscosity and slurry stability of leached kaolin clays, and the improved products thus formed are disclosed. The process involves the addition of phosphoric acid as a clay flocculant to a clay slurry during leaching with known leaching compounds, such as compounds containing an active 0 group, to yield a finished clay product that, upon dispersion, possesses a lowe viscosity and improved slurry stability. Through the practice of the invention, a washing step and/or a second filtration step, sometimes considered necessary in conventional kaolin processing for removal of excess soluble salts to obtain minimum viscosities and adequate slurry stability, is obviated.

11 Claims, 4 Drawing Figures FLOCCULATION OF KAOLIN SLURRIES WITH PHOSPHORIC ACID BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to kaolin clay products and, more particularly, pertains to a process for improving the viscosity and slurry stability of leached kaoline clays and the improved products thus produced.

2. Description of the Prior Art Many natural kaolin clays, as mined, are discolored by the presence of iron-stained titaniferous mineral contaminants. It is common practice in the industry to upgrade the color of natural clays by treating the clays with leaching agents to reduce some portion of the color contaminants to soluble salts that can be removed by filtration and/or washing of the leached clays. Generally, the most conventional leaching procedure is to form an aqueous suspension of the clay after coarse contaminants have been removed, acidify the slurry to a pH of from about 3.0 to 4.5 and to add a leaching compound or agent. There are many leaching or reducing agents known in the art, e.g., dithionite leaching compounds and the like. Presently, it is common practice in the industry to employ dithionite leaching compounds containing an active group or a combination of chemicals known to liberate such a group. In addition, in present practice the acidification step is normally accomplished by the addition of flocculating agents such as aluminum sulfate, sulfuric acid, hydrochloric acid, and the like. After leaching, the clay is filtered to remove soluble salts, dispersed or washed, and dried by conventional means.

There are many prior art variations of the abovedescribed somewhat conventional leaching process. For example, British Patent No. 929,539 teaches a process for leaching natural kaolin clays where a trivalent titanium salt is utilized as the leaching or reducing agent. Urfer et al., in U.S. Pat. No. 3,043,707, teach the utilization of orthorhombic phosphorous pentoxide as an acidulating and deflocculating agent in leaching clay slurries. Pantentees disclose a process wherein the orthorhomic phosphorous pentoxide is added to an acidified leached clay slurry, leached with a conventional hydrosulfide leaching agent, to improve leaching and to lower the slurry viscosity.

ln addition, British Patent No. 1,041,560, and its Canadian counterpart, Canadian Patent No. 748,473, teach a process for leaching kaolin clay having approximately the same water content as when mined, e.g., clays containing from to 40 percent by weight of water. The references teach a process whereby the low water content clay is first acidified with a non-oxidizing mineral acid, such as ortho-phosphoric acid. The leaching process is carried out in a pug-mill or suitable apparatus for thoroughly mixing materials having a plastic consistency. A solution of a salt of dithionous acid is then added to the acidified clay. The references disclose that the process improves brightness of the clay without requiring the formation of a clay slurry prior to leaching.

As is known in the art, it is preferred that refined leached kaolin clays, especially those to be employed in the coating of paper, have definite and uniform low viscosity properties upon dispersion. It is also preferred that the refined clays, upon dispersion, have a stable viscosity during storage. However, the known prior art processes for leaching kaolin clays mentioned hereinabove primarily have the common disadvantage of producing resulting clays that upon dispersion possess high viscosities and poor slurry stabilities. This is presumed to be due to one or more basic factors including, for instance, the nature of the crude clay from which it originates, the soluble salt content remaining after filtration, excess leach dosage, incomplete reaction of chemical products and the like. Therefore, in order to provide refined, leached kaolin clay products that, upon dispersion, have adequate low viscosities and slurry stability it has become a practice in the industry, when conventional leaching processes are utilized, to sometimes wash the leached clays to remove excess soluble salts not removed by initial filtration. This is usually done by reslurrying or washing the filter cake after leaching and filtering a second time. As should readily be appreciated by those skilled in the art, such techniques, i.e., washing and then filtering a second time, is time consuming, costly and highly undesirable. On the other hand in the practice of the present invention these disadvantages are overcome.

SUMMARY OF THE INVENTION The present invention provides a highly efficient process for improving the viscosity and slurry stability of leached kaolin clays. The invention is based upon the discovery that the viscosity of a finished clay product can be significantly reduced and the overall rheological properties of dispersed aqueous slurries of such clays greatly improved by the addition of phosphoric acid, as a flocculating agent, to aqueous clay slurries leached with known leading compounds, e.g., a compound containing an active (8 0 group or a compound capable of liberating such group in the slurry. Generally, the inventive process comprises forming an aqueous kaolin clay slurry, adding a known leaching compound thereto, and then adding phosphoric acid in an amount sufficient to lower the pH of the slurry to within the range of about pH 2.5 to about 4.5 during the leaching step. The resulting leached slurry can then be dewatered, such as by filtration, to remove soluble salts, contaminants and the like to yield a finished clay product which, upon dispersion, possesses a lower viscosity and improved slurry stability upon standing in an aqueous solution, yet the natural brightness of the finished clay product is not substantially reduced, if at all, when compared to finished clays prepared by known prior art leaching processes.

In the practice of the invention, the need for a second filtration step to provide an adequate low viscosity and stability when the clays are leached by known prior art processes, is obviated. Thus, the invention provides a significant savings in labor and overall time required to produce high grade kaolin clays, such as may be required in coating paper and the like.

lt is accordingly a general object of this invention to provide a unique process for reducing the viscosity and improving the stability during storage in an aqueous solution of leached kaolin clays.

Another and more particular object of this invention is to provide a highly efficient and economical method for improving the viscosity and slurry stability of a leached kaolin clay, which method eliminates the requirement of a double filtration step.

It is a further object of the instant invention to present an improved process for leaching kaolin clays that produces a resultant finished clay product which, upon dispersion, exhibits viscosities, brightnesses, slurry stabilities and overall rheological properties comparable to or superior to finished clay products leached by conventional processes wherein the processes include the additional steps of washing and refiltering the leached clays to provide desirable low viscosities and stability.

Yet another object of this invention is to provide a method whereby leached clay slurries which now require two consecutive filtration steps, can be filtered only once and still yield an acceptable product having coating properties comparable to conventionally processed clays.

Other objects and advantages of the invention, if not set forth specifically herein, will become readily apparent from the ensuing descriptions of the drawings and the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS The manner in which the foregoing and other objects are achieved in accordance with the present invention will be better understood in view of the following detailed description and accompanying drawings, which form a part of this specification and where:

FIGS. 1 and 2 are graphs illustrating the effect of increasing the amount of the leaching compound on the low shear (Brookfield) and high shear (Hercules) viscosities of a Central Georgia kaolin clay when employing phosphoric acid or aluminum sulfate as the flocculating agent at a constant pH; and

FIGS. 3 and 4 are graphs illustrating the effect on the low and high shear viscosities of a Central Georgia kaolin clay when the pH, determined by the amount of flocculant employed, of the clay slurry is varied while the amount of the leaching compound is held at a constant level. The use of phosphoric acid and aluminum sulfate as the flocculant are compared similarly as in FIGS. 1 and 2.

The reference characters of FIG. 1, denoting the recited test samples are similarly employed in FIGS. 2-4.

DESCRIPTION OF THE PREFERRED EMBODIMENT As mentioned hereinbefore, the present invention pertains to a process wherein phosphoric acid is added to an aqueous clay slurry being leached with known leaching compounds as a clay flocculant to bring about a combined effect with the leaching chemicals to yield a finished clay product exhibiting improved lower viscosity and slurry stability properties. More particularly, crude kaolin clay taken from the mine is first blunged" in water to form a slip or slurry. A suitable dispersant, such as sodium hexametaphosphate, sodium tripolyphosphate or the like may be added, if desirable, at this point to increase the fluidity of the suspension and enable the maximum quantity of clay to be processed, as is known in the art. The fluid slip may then be passed through sand boxes or screens to remove coarse impurities. After degritting" in this manner, the clay suspension is fractionated in accordance with known techniques and the fine fraction, still in suspension, is in condition for leaching employing known leaching agents.

Turning now to more specific details of the invention, although the percent solids (clay) in the clay-water suspension may vary, particularly advantageous results are obtained when the slurry contains from about '10 to about 35 percent clay solids, by weight. The inventive process is especially applicable to slurries having 25 to 35 percent clay solids, by weight. The leaching chemical and the phosphoric acid flocculant are then incorporated into the kaolin clay slurry in accordance with the instant invention.

While any of the known leaching agents may be used, preferably sodium or zinc dithionite is employed. The particular amount of dithionite added is, of course, dependent upon the severity of discoloration of the kaolin clay being leached and is usually determined empirically. In addition, the quantity is dependent upon the type of dithionite employed. Experience has shown that the addition of from about three to about ten pounds of zinc or sodium dithionite per ton of kaolin clay being treated usually provides adequate leaching, with five to about eight pounds, per ton of clay, of zinc or sodium dithionite normally being optimum for leaching a kaolin clay.

Although the phosphoric acid flocculant may be added substantially simultaneously with the leaching chemical and substantially improved viscosity characteristics will result, in order to accomplish all objectives of the invention, the phosphoric acid should be added after the incorporation of the leaching compound into the slurry as will be more particularly discussed hereafter. The amount of phosphoric acid added to the leachclay slurry mixture is preferably an amount sufficient to lower the pH of the mixture to within the range of about pH 2.5 to 4.5. The optimum pH range is between about pH 3.5 to about pH 4.5. It has been found that the addition of about /2 to l5 pounds phosphoric acid (on a 100% H PO basis) per ton of the kaolin clay will usually sufficiently lower the pH of the leach-clay slurry to within the described pH range of about 3.5 to 4.5, the particular amount being dependent upon the particular type of clay and leaching compound being employed and is best determined empirically. Although any desirable concentration of phosphoric acid reagent may be utilized, we prefer to employ phosphoric acid having a concentration on the order from about percent to about percent by weight.

Preferably, the leaching chemical and the phosphoric acid flocculant are added to the slurry while agitating the suspension. A particular rate of agitation or agitation time during and following the addition of ingredients is not critical except insofar as the latter must be sufficient for the leach reaction to reach completion. In general, agitation from 20 to 50 minutes is satisfactory with 25-30 minutes being the preferred time. Any conventional agitation apparatus may be utilized that will produce adequate mixing of added compounds and slurry.

As briefly mentioned hereinabefore, although the improved lower viscosities and slurry stability are obtained when phosphoric acid is added substantially simultaneously with the leaching chemicals to the clay slurries, a loss in maximum brightness is also obtained on some clays, as compared to the maximum brightness of clay slurries leached and flocculated with conventional flocculants, such as aluminum sulfate, sulfuric acid, and the like by conventional processes. However, most unexpectedly, we have found that by the addition of the phosphoric acid after the leaching compound has been added to the clay slurry, but still during the leaching step, the loss of maximum brightness is substantially reduced, if not completely eliminated. This phenomenon is most evident when the leaching chemical, such as zinc or sodium dithionite, is allowed to react with the kaolin clay slurry for about 5 to minutes prior to phosphoric acid addition, with about 10 minutes being optimum. The resultant finished clays have brightness substantially comparable to finished clays flocculated with aluminum sulfate which have been double filtered in accordance with conventional procedures. Additionally, experiments have shown that coating properties of the resultant clays are substantially comparable to double filtered alum flocculated clays in regard to brightness, gloss, printed gloss, opacity, whiteness, ink absorption and the like.

Furthermore, although in the preferred embodiment of the present invention, phosphoric acid is added to a leachclay slurry mixture as a flocculant alone, it will be understood that phosphoric acid can be utilized in combination with known conventional flocculants such as aluminum sulfate, sulfuric acid, hydrochloric acid, etc. For example, phosphoric acid can be combined with aluminum sulfate and employed as the flocculant to produce a finished clay product having improved lower viscosity and slurry stability properties. The particular ratios of phosphoric acid to conventional flocculant employed is primarily dependent upon the properties desired in the finished clay product, so long as the combinations of the flocculants are added in amounts sufficient to lower the pH of the slurry to within the above-described pH range. However, experiments have shown that when the ratio of phosphoric acid to conventional flocculant, e.g. aluminum sulfate, employed decreases, there is a proportional increase in viscosity of the finished clay, upon dispersion. Accordingly, in the practice of this particular embodiment of the invention, wherein phosphoric acid is employed in combination with aluminum sulfate, the phosphoric acid should be added in an amount of at least about twenty-five percent, by weight of the flocculant used. Test results have indicated that about twenty-five percent phosphoric acid, by weight of flocculant, is approximately the minimal amount that can be employed to provide adequate viscosity reduction and slurry stability properties in the finished clays.

As briefly discussed hereinbefore, after phosphoric acid flocculant addition, the leached clay slurry is then dewatered or filtered to remove soluble salts therefrom. Any conventional filtration process and apparatus can be employed. The resulting filter cake may then be dispersed and dried by conventional means or dispersed and stored in slurry form. In this regard, in known leaching processes it has been difficult to achieve a low enough level of soluble salts for maintaining a sufficient viscosity for shipment. This problem is especially disturbing with clays that require excessive amounts of leaching chemicals to obtain suitable coating properties. Thus, in the past it has been necessary to reslurry the filter cake and to refilter to obtain adequate soluble salt removal. Through the practice of this invention, these conventional procedures are obviated.

After filtration, the filter cake is preferably dispersed by the addition of a suitable dispersant to increase the fluidity of the suspension. Any conventional dispersant can be utilized, such as tetrasodium pyrophosphate, sodium hexametaphosphate, sodium tripolyphosphate and the like. The addition of a dispersant is preferably carried out before the drying step, or the drying step may be completely eliminated where the finished clay product is to be shipped and/or stored in slurry form.

As will be further and more fully illustrated by the following examples, the present invention overcomes the disadvantages of the prior art. While particularly advantageous method embodiments have been set forth in the examples, they are intended to illustrate the invention and not to limit it thereto. ln the following examples, most of the data showing the comparison of phosphoric acid with other flocculants is stated in pH. Quantities of the compounds are generally not comparable because any specific flocculant will require a different dosage to reach a specific pH, depending upon its acidifying ability.

EXAMPLE I A degritted, fractionated Central Georgia kaolin fraction of 80 percent less than 2 microns was slurried to 28 percent by weight solids and, with agitation, leached by the addition of 8 pounds ZnS O /ton of clay. The combined mixture was then flocculated by the addition of 6 pounds alum (aluminum sulfate, pH 4.0). Agitation was continued until leaching was completed, taking about 25-30 minutes. The combined slurry was then filtered employing a rotary filter and the filter cake dispersed to minimum viscosity. The resulting low shear, Brookfield viscosity was 207 cps. and the high shear, Hercules viscosity was 14.0 dynes at 1,100 rpm, at 70 percent solids.

The above procedure was repeated except that the clay slurry was leached by the addition of 8 pounds I ZnS O, per ton and flocculated by the addition of 3.1

pounds H SO, (pH-4.0) per ton, respectively. Upon dispersion to minimum viscosity, the low shear Brookfield viscosity was 189 cps. and the high shear Hercules viscosity was 12.6 dynes at 1,100 rpm, at solids.

The above procedure was again repeated except that EXAMPLE II A degritted, fractionated Central Georgia kaolin fraction of percent less than 2 microns was slurried (28 percent by weight solids), and leached by conventional means with the addition of 6 pounds/ton kaolin of Na S O Six pounds/ton kaolin of alum (pH 4.2) was added to the slurry and the combined mixture agitated for about 25-30 minutes. The slurry was then filtered and the filter cake dispersed by reslurrying to minimum viscosity. At 70 percent solids minimum viscosity the low shear, Brookfield viscosity, was 172 cps. and the high shear, Hercules viscosity, was 12.6 dynes/1,100 rpm.

The process was repeated on another Na S O slurry mixture and with 2.9 pounds/ton clay of H SO, (pH 4.2) being added as the flocculant. After filtration,

7 8 dispersion and adjustment to 70 percent solids, the re- Example II) viscosity (at 70 percent solids) using phosfined slurry exhibited minimum viscosities of 170 cps. phoric acid as a flocculant is shown in FIGS. 1 and 2. Brookfield and 13.0 dynes/l ,100 rpm Hercules As shown, these results are compared with leached clay The procedure was again repeated employing still anslurries similarly prepared with alum (aluminum sulother slurry of the same clay leached with the same fate) employed as the flocculant. Also disclosed is the amount of Na s o H B 1 0 was dd d as h outcome of double filtering the aluminum sulfate flocflocculant to the slurry during leaching in an amount chimed y- Optimum brightness for this y was sufficient to lower the pH of the slurry to 4.2. After filmined at a leach dosage of 6 Pounds 2 4 p ton of tration, dispersion and adjustment to 70 percent solids, clay- The afhouht Offlocchlaht p y was held the final clay slurry viscosity was 106 cps. Brookfield l0 Siam at either p h alhfh/toh or POuhdS d 8 I /1 100 rpm Hercules H PO /ton of clay, wh1ch prov1ded average pHs of about 4.2 and 4.0 respectively. EXAMPLE These results indicate that the use of phosphoric acid A degritted, fractionated East Georgia kaolin fracwith only a Single filtration yields essentially the Same i f 92 95 percent less than 2 microns was slurried Hercules viscosities and almost equivalent Brookfield' b Conventional means to provide a s|urry Containing viscosities as the double filtered finished clay products about 28 percent by weight clay solids. A portion of the even e the leach Chemical dosage is slurry was separated and treated with 6 pounds f over, as lllustrated, the effect of the phosphoric ac1d 2 5 0 per ton f clay and 45 pounds f alum/ton flocculation upon viscosity becomes more pronounced clay, the alum being added during leaching with agitaas the leach dosage Increased beyond Ophmumtion (sampleA). A second portion of the clay slurry EXAMPLE V was treated 1n the same manner, 1.e., 51X pounds of z s o added, except that pounds HZSOMO Several test samples of leached clay (Central Georgra was employed i place f alum (Sample B) A third pop kaolin) slurries were prepared generally in accordance tion of the same clay slurry was similarly treated with whh the P e of Example h empleylhg 2 4 35 2 5 0 except that 9 pounds pom was added as the leach chem1cal and H PO and alummum as respecthe fl l t during leaching (sample C) All samples tive flocculants. In each test sample the ZnS O ut1l1zed (AL 5 and (C) were filt d and dispersed to mini was held constant at 8 pounds ZnS O per ton of clay mum viscosities (70 percent solids) in the same manner However the amount of flocculant 3 4 except that, prior to dispersion, equal portions of both aluhhhum sulfate) added to h salhple Vaned (A) and (B) were Separated reslurried and refiltered whlch resulted n S lUTI'IES with differing pH s. After to produce Samples (D) and The effectiveness of leachmg, w1th ag1tat1on, for about 25-35 mmutes, each each treatment procedure upon initial viscosity and Sample was hhered- The fiher cake h halhthe alum slurry stability is shown in the following Table l. fl fl ate mp e wsti th mfilaws K TABLE 1 VISCOSITY PROPERTIES OF EAST GEORGIA KAOLlN FRACTION Dispersed Minimum Brookfield Viscosity, cps. at 70% Solids After 3 days After 7 days As is illustrated in Table 1, the utilization of phos-. and filtered asecond time. All samples were finally disphoric acid as a flocculant (C) in the leaching of kaolin persed and adjusted to 70 percent solids slurries. The

provides an improved lower initial viscosity and imlow and high shear viscosities of each sample were then Proved Slurry Stability as compared to identically W 1 tested per Example I and plotted versus the pH detercessed leached kaolin slurries wherein alum (A) or Sulmined by H PO and alum flo cula t additi Th furic acid (B) is added as the flocculating agent. Moresults have been illustrated in FIGS, 3 and 4,

over, the phosphoric acid flocculated finished clay As shown in FIGS. 3 and 4, the use of phosphoric slurry (C) has an initial viscosity and storage stability acid as a flocculant with only a single filtration in a substantially comparable to an alum flocculated kaolin wide range of amounts produces finished clay slurries slurry (D) that has been reslurried and filtered a second having greatly superior low and high shear viscosities ti Still f th th ph phoric acid flocc lated clay than single filtered finished slurries flocculated with' slurry has superior low initial viscosity and slurry storcomparahlfi amounts of alum- MQl'em/er, h a p age stability as compared to a sulfuric acid flocculated flocculated Samples have low and h Shear VlSCOSItIBS l slurry (E) h h b d bl fil d substantially equal to and superior, respect1vely, to

. double filtered alum flocculated samples. EXAMPLE I\/ 5 7 EXAMPLE VI The effect of increasing the leach chemical dosage on a clay slurry (same type as employed and prepared ir In a series of tests, a Central Georgia clay slurry (9O percent less than 2 microns) of 28 percent solids, prepared per Example II, was utilized. Tests were conducted employing the following three conditions:

A. Single filtered, flocculated with alum B. Double filtered, flocculated with alum C. Single filtered, flocculated with phosphoric acid Leaching of each test sample was performed with the addition of 7.5 pounds ZnS O /tn and then sufficient flocculant was added to obtain a pH of 4.3 per Example II. All test samples were then filtered, dispersed and minimum viscosities adjusted to 70 percent solids in the same manner except that test sample 3" included an additional filtration step. The samples were then analyzed for minimum viscosity and slurry stability at 130F. The results of the tests are shown in Table 2.

A Central Georgia kaolin fraction of 9071 less than 2 microns sold under the trademark hydrafine" by the J. M. Huber Corporation.

Table 2 illustrates minimum viscosity and slurry stability properties of a single filtered, phosphoric acid flocculated clay are greatly improved as compared to said properties of single filtered, alum flocculated clay and substantially equivalent to the double filtered, alum flocculated clay.

EXAMPLE VII In a series of tests, an East Georgia kaolin slurry TABLE 3 VISCOSITY PROPERTIES OF HYDRAGLOSS Test No. A B C Floceulant Used Alum Alum H PO No. of Filtrations One Two One Minimum Viscosity at 70.571 Solids Brook rcld, cps 252 2] I 230 Hercules. dyncs/l I00 rpm [.9 1.8 L8 Slurrv Stability at I30F Brookfield Viscosity cps After 3 Days 930 31] 383 After 7 days 4240 I030 1880 An East Georgia kaolin fraction of 92-95% less than 2 microns sold under the trademark H \'dragloss by the .l. M. Huber Corporation.

Table 3 illustrates the physical properties of the clays. The single filtered, phosphoric acid flocculated clay is essentially equivalent to the double filtered alum flocculated control in both minimum viscosity and slurry stability. On the other hand, it is superior to single filtered, alum flocculated clay.

EXAMPLE VIII To illustrate the improvement in viscosity and slurry stability obtained by the use of phosphoric acid as a flocculant even in blends with conventional flocculants, a series of tests were made by blending alum and H PQ, in varying proportions and utilizing the blends as the flocculating agent. A slurry of Central Georgia kaolin fraction of 80 percent less than 2 microns having 30 percent by weight solids was prepared in accordance with the process of Example I. Test samples of the slurry were leached by the addition of 6 pounds ZnS O /ton. During leaching, a blend of alum and phosphoric acid, in varying proportions, was added to 5 each test sample in an amount sufficient to adjust the (Q2-95 cent less than 2 microns) of 25 percent 40 pH of the slurry mixture to about pH 4.4. The samples were filtered, dispersed, and analyzed for viscosity and slurry stability in a like manner. The results are shown in Table 4. V

TABLE 4 PHYSICAL PROPERTIES OF KAOLIN CLAY FLOCCULATED WITH BLENDS OF ALUM AND HQPOI Test No. I 2 3 4 5 of Floceulant Used gBy Weight) Alum 100 75 25 H PO 25 50 75 I00 Minimum Viscosity at 70% Solids Hercules, dynes/I I00 rpm 14.0 8.8 5.6 5.5 5.0

Slurry Stability at I30F Brookt'ield Viscosity c s After 3 Days 280 207 195 188 136 After 7 Days 462 3IO 276 I88 I68 solids was prepared in the same manner as set forth in The above results indicate that the viscosity and Example Ill. Tests were made on the clay slurry using slurry stability of the clay is proportionately improved the following three conditions:

A. Single filtered flocculated with alum B. Double filtered flocculated with alum C. Single filtered flocculated with phosphoric acid Three test samples ofthe clay slurry were leached by the addition of 6.3 pounds ZnS O /ton followed by flocculant addition in amounts sufficient to lower the pH of the slurries to about 4.2. These samples were then filtered, dispersed and analyzed for minimum viscosity and slurry stability per Example VI. Results of the tests are shown in the following Table 3.

with the use of increasing amounts of phosphoric acid as the flocculant.

EXAMPLE IX about 5 to 15 minutes (preferably about 10) after the addition of the leach chemical. The results of Table 5 were obtained by treating the same type clay slurry prepared in Example II. Leaching was accomplished by the clay water slurry with about 3 to about l pounds, per ton of clay, ofa leaching agent capable of reducing the insoluble salts present in said slurry as impurities to their soluble form. flocculating said slurry with a flocaddition of 6 pounds ZnS O /ton to said slurry. culatingagent, and dewatering the resultant slurry mix- TABLE 5 SEQUENCE OF LEACH AND FLOCCULANT ADDITION TO KAOLlN CLAY Minimum Time Allowed for Leach Brookfield Vis- Flocculant to React Prior to Floc- Brightcosity at 70% Sample Used culant Addition, Mins. ness Solids. cps.

1(Control) Alum None (Added Together) 89.3 I62 2(Control) Alum 89.2 167 3 H31704 None (Added Together) 88.8 133 4 H3PO4 5 89.0 130 5 11,,Po, 10 89.3 125 6 11,,Po, 89.2 128 7 HQPO, Leach added 10 mins.

after H PO, 87.8 128 EXAMPLE X ture to remove said soluble salts, the improvement To determine the physical properties of a Central ccmpilsmgz Georgia coating clay leached and flocculated to a pH addmg phosPhonc acld as 1 flocculatmg agent to i of about 2 to 3 by a H PO the following experiment m (.iurmg leachmg Step i phosphoric was conducted. A slurry of a Central Georgia kaolin acld bemg added m an amount sufficlem to reduce fraction of 80 percent less than 2 microns having 30.66 the PH of the slurry between about to about percent solids, by weight, was prepared in accordance to .therel.)y Obtain a finished clay prodlict h with the process of Example I. Individual samples ofthe upon pt possesses T F low vscosny slurry were leached by the addition of 6 pounds lf f lfll ty 121251551 21251. ZnS O,/ton of clay and varying amounts of alum or A method for improving the Viscosity and y- H PO to obtai th d i d E h Sample was i stability of kaolin clays leached to remove color impugle-filtered, dispersed to minimum viscosity and spray Titles therein, Said method Comprising! dried prior to physical testing. The results are set av forming an aqueous Slurry of a finely divided forth in Table 6. olin clay; 7

TABLE 6 EFFECT OF LEACHlNG WITH PHOSPHORIC AClD AT LOW H's Test No. 1 2 3 4 5 6 Floeculant Used Alum Alum H m, H PO, HJO, 1-1,?0 pH Prior to Filtration 4.5 4.0 4.5 4.0 3.0 2.0 Amount of Flocculant No./ton clay 5.0 11.0 2.2 3.7 9.4 85.2 m

Brightness, 86.6 86.3 86.0 86.0 86.3 85.5 Min. Viscosity at 70% Solids:

Brookfield, cps 220 258 138 148 148 1200* Hercules. dynes/rpm l8+l730 18-1-1730 18+/1075 l8+/l075 l8+l9l5 Al solids of only 64.4 H

The above results illustrate that H PO flocculated clays produce a substantial reduction in viscosity as compared to alum flocculated clays at the same pH. In addition, it can be seen that reduction in viscosity is obtained by employing H PO up to an amount that willprovide a pH somewhere between pH 2 and 3. At pH I claim: 1. ln the method for producing high grade kaolin clay.

products which comprises leaching a dispersed kaolin b. contacting said aqueous slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing insoluble salts present in said slurry to a soluble form, said leaching agent comprising a compound containing an active (8 0 group or a compound capable of liberating such group in said slurry; adding phosphoric acid as a flocculant to the slurry-leaching agent mixture, said phosphoric acid being added in an amount sufficient to lower the pH of said mixture to between about pH 2.5 to about pH 4.5; and d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses improved low viscosity and slurry stability during storage.

3. The method in accordance with claim 2, wherein said leaching agent is a compound selected from the group consisting of sodium dithionite and zinc dithionite.

4. The method in accordance with claim 2, wherein said phosphoric acid is added in an amount sufficient to lower the pH of the slurry leaching agent mixture to between about 3.5 to about 4.5.

5. The method in accordance with claim 2, wherein said phosphoric acid is added at least about minutes after the beginning of the leaching step to thereby obtain maximum brightness of the finished clay product as well as said improved viscosity and slurry stability.

6. A method in accordance with claim 2, wherein said phosphoric acid is added in an amount of from about /2 to about pounds phosphoric acid per ton of the kaolin clay.

7. The method in accordance with claim 2, wherein said slurry contains from about 10 to 35 percent clay solids, by weight.

8. The method in accordance with claim 2, wherein said phosphoric acid is employed as said flocculant in combination with a flocculant selected from the group consisting of aluminum sulfate, sulfuric acid, or hydrochloric acid.

9. The method in accordance with claim 8, wherein said phosphoric acid is added during the leaching step in combination with aluminum sulfate.

10. A method in accordance with claim 9, wherein at least about twenty-five percent by weight of said phosphoric acid-aluminum sulfate mixture is phosphoric acid.

1 1. A high grade kaolin clay product which, upon dispersion, possesses improved low viscosity and slurry stability during storage in an aqueous solution, said kaolin clay product being prepared by the method comprising the steps of:

a. forming an aqueous slurry of a finely divided kaolin clay;

b. contacting said clay water slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing the insoluble salts present in said slurry to their soluble form, said leaching agent being selected from the group consisting of sodium dithionite and zinc dithionite;

. adding phosphoric acid as a flocculant to the slurry during the leaching step in an amount sufficient to lower the pH thereof to between about pH 2.5 to about pH 4.5, said acid being added after the leaching step begins; and

d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses low viscosity and improved slurry stability.

33 UNITED STAS MTENT OFFICE CERTIFICATE @F CECT ION Patent No. 3,849,151. Dated'Novemj er 19, 1974 Inventofls) William Abercrombie, Jr.

It is certified that errpr appears in the ebcve-identified petent; andthat said Lettere' Patent are hereby ccri'ecte ee shown helm;

. On thec ei page 'of Pateh't,' in" the right "hand column,

in *Abstx act, line 8, cancel "'lowe" and substitute 5.8 cancel "hereihabeforei andhsubsti tute 1 'herei nbefore f-r. I I v c 1 I Tahle 'lfcancel ""vi'sco sity, cps. at 70% Solids "on the le f-t side -of-ithetable and substitute Viscosity, :cps, at 70% S'olid's' on the right handfside; 'cf the table inune'dia'tel belcw Dispersed'T-Minfjghumprookfield.

Incolpmnll-,5 6-,}ffund er zAmount 'f oif Fl occul ant cancel n= ,en ll's ilfwt L S' 'Q Y I sign d i d se ajl' e d'} 11th day of March 1975.

v c'. MARSHALL DANN RUTH"C "z Commissioner of Patentst s l g Q fi ice'r' Y f and Trademarks 

1. IN THE METHOD FOR PRODUCING HIGH GRADE KAOLIN CLAY PRODUCTS WHICH COMPRISES LEACHING A DISPERSED KAOLIN CLAY WATER SLURRY WITH ABOUT 3 TO ABOUT 10 POUNDS, PER TON OF CLAY, OF A LEACHING AGENT CAPABLE OF REDUCING THE INSOLUBLE SALTS PRESENT IN SAID SLURRY AS IMPURITIES TO THEIR SOLUBLE FORM, FLOCCULATING SAID SLURRY WITH A FLOCCULATING AGENT, AND DEWATERING THE RESULTANT SLURRY MIXTURE TO REMOVE SAID SOLUBLE SALTS, THE IMPROVEMENT COMPRISING: ADDING PHOSPHORIC ACID AS A FLOCCULATING AGENT TO SAID SLURRY DURING THE LEACHING STEP, SAID PHOSPHORIC ACID BEING ADDED IN AN AMOUNT SUFFICIENT TO REDUCE THE PH OF THE SLURRY TO BETWEEN ABOUT 2.5 TO ABOUT 4.5, TO THEREBY OBTAIN A FINISHED CLAY PRODUCT THAT UPON DISPERSION, POSSESSES IMPROVED LOW VISCOSITY AND SLURRY STABILITY CHARACTERISTICS.
 2. A method for improving the viscosity and slurry stability of kaolin clays leached to remove color impurities therein, said method comprising: a. forming an aqueous slurry of a finely divided kaolin clay; b. contacting said aqueous slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing insoluble salts present in said slurry to a soluble form, said leaching agent comprising a compound containing an active (S2O4) group or a compound capable of liberating such group in said slurry; c. adding phosphoric acid as a flocculant to the slurry-leaching agent mixture, said phosphoric acid being added in an amount sufficient to lower the pH of said mixture to between about pH 2.5 to about pH 4.5; and d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses improved low viscosity and slurry stability during storage.
 3. The method in accordance with claim 2, wherein said leaching agent is a compound selected from the group consisting of sodium dithionite and zinc dithionite.
 4. The method in accordance with claim 2, wherein said phosphoric acid is added in an amount sufficient to lower the pH of the slurry leaching agent mixture to between about 3.5 to about 4.5.
 5. The method in accordance with claim 2, wherein said phosphoric acid is added at least about 5 minutes after the beginning of the leaching step to thereby obtain maximum brightness of the finished clay product as well as said improved viscosity and slurry stability.
 6. A method in accordance with claim 2, wherein said phosphoric acid is added in an amount of from about 1/2 to about 15 pounds phosphoric acid per ton of the kaolin clay.
 7. The method in accordance with claim 2, wherein said slurry contains from about 10 to 35 percent clay solids, by weight.
 8. The method in accordance with claim 2, wherein said phosphoric acid is employed as said flocculant in combination with a flocculant selected from the group consisting of aluminum sulfate, sulfuric acid, or hydrochloric acid.
 9. The method in accordance with claim 8, wherein said phosphoric acid is added during the leaching step in combination with aluminum sulfate.
 10. A method in accordance with claim 9, wherein at least about twenty-five percent by weight of said phosphoric acid-aluminum sulfate mixture is phosphoric acid.
 11. A high grade kaolin clay product which, upon dispersion, possesses improved low viscosity and slurry stability during storage in an aqueous solution, said kaolin clay product being prepared by the method comprising the steps of: a. forming an aqueous slurry of a finely divided kaolin clay; b. contacting said clay water slurry with from about 3 to about 10 pounds, per ton of clay, of a leaching agent capable of reducing the insoluble salts present in said slurry to their soluble form, said leaching agent being selected from the group consisting of sodium dithionite and zinc dithionite; c. adding phosphoric acid as a flocculant to the slurry during the leaching step in an amount sufficient to lower the pH thereof to between about pH 2.5 to about pH 4.5, said acid being added after the leaching step begins; and d. dewatering the resultant mixture to thereby obtain a finished clay product that, upon dispersion, possesses low viscosity and improved slurry stability. 